I’d be interested in how your privacy policy allows this. I can’t find where it mentions photos are stored or used for training purposes…
I would be more interested on why you believe something like this isn't baked into most privacy policies.
I'm not shocked but I'm shocked you are shocked.
The MyFitnessPal privacy policy says "We use photos, videos, or other data you provide to us to customize our Services." [1]
That's all they need to do to cover themselves.
[1] https://www.myfitnesspal.com/privacy-policy